High efficiency permanent magnet meter

ABSTRACT

A permanent magnet meter for providing a scale indication of the magnitude of an electrical signal. The meter comprises a permanent magnet rotationally supported by a plurality of thin vanes loosely fitted through slots therein to allow rotation of one vane with respect to another. An arctuate flux path of high permeability material is spaced from the permanent magnet to receive the magnetic flux through an air gap which increases with rotation of the magnet. The magnetic force between the magnet and flux path torques the magnet to a position of minimum air gap and biases the vanes pivots to minimize the motion resulting from the looseness of fit between the vanes. An electrical coil is wound about the flux path and responds to the electrical signal being measured to provide a flux in the path counteracting that from the permanent magnet and causing rotation of the permanent magnet to a point of equilibrium at a new angle defined by an alteration in the permanent magnet flux in response to the coil induced flux.

United States Patent 91 Mason 1 Oct. 9, 1973 1 HIGH EFFICIENCY PERMANENTMAGNET METER [75] Inventor: David P. Mason, Braintree, Mass.

[73] Assignee: Beetle Electrical Instrument Co.,

Inc., Penacook, NH.

[22] Filed: Dec. 23, 1971 [21] Appl. No.: 211,477

[52] US. Cl. 324/146, 324/154 PB Primary Examiner--Alfred E. SmithAttorney-Joseph Weingarten et a1.

57 ABSTRACT A permanent magnet meter for providing a scale indication ofthe magnitude of an electrical signal. The meter comprises a permanentmagnet rotationally supported by a plurality of thin vanes looselyfitted through slots therein to allow rotation of one vane with respectto another. An arctuate flux path of high permeability material isspaced from the permanent magnet to receive the magnetic flux through anair gap which increases with rotation of the magnet. The magnetic forcebetween the magnet and flux path torques the magnet to a position ofminimum air gap and biases the vanes pivots to minimize the motionresulting from the looseness ,of fit between the vanes. An electricalcoil is wound about theflux path and responds to the electrical signalbeing measured to provide a flux in the path counteracting that from thepermanent magnet and causing rotation of the permanent magnet to a pointof equilibrium at a new angle defined by an alteration in the permanentmagnet flux in response to the coil induced flux.

25 Claims, -10 Drawing Figures PAIENTEUHBI elm 3.764.910

" sumlurg B FLUX DENSITIES IO,OOO

FIELD INTENSITY FIG.3

Pmmznnm 1 3.764.910

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1 HIGH EFFICIENCY PERMANENT MAGNET METER FIELD OF THE INVENTION Thisinvention relates to the measurement of electricity and in particulartometers indicating the magnitude of an electrical signal.

BACKGROUND OF THE INVENTION In the design of an electric meter severalbasic functions combine to provide a practically operating meter whosedeflection increases with the magnitude of an electrical signal. Thesefunctions include motivation to cause deflection of the meter elementsin response to the electrical signal, restoration which counteracts themotivation, and the suspension which rotationally or otherwise supportsthe meter movement and its associated pointer. These functions arenecessary in any meter, and the precision with which they operatedetermines meter accuracy, while the complexity of the design determinescost. It is desirable then to provide a meter design where thesefunctions are accomplished as simply and precisely as possible with eachmeter component cooperating toward total meter functioning and notcreating further problems which require complex and expensivecompensating designs.

In the DArsonval meter, one of the commonly found meter types, most ofthese features are provided by independently operating, complexelements. For example, suspension is commonly provided by a precisionpivot and jewel mechanism. Motivation is the result of the interactionbetween current in a moving coil and a magnet field where the coildesign is not readily mass produced or assembled. The restoring force,and application of the signal to the motivation source is achieved by aspring mechanism, commonly one or more delicate spiral bands connectedbetween the moving coil and meter casing. Where the filar suspension isused, some design simplification is possible, but a greater vibrationalsensitivity results often necessitating ackward damping techniques.

Thus, while the DArsonval meter is capable of very accurate measurementsof electrical magnitudes, this accuracy is achieved at great cost owingto the complexity of the meter elements necessary for precise andconsistent operation.

As a less costly alternative to the DArsonval meter, the less accurateand less efficient moving magnet meter design may be used. In thesemeters, a large permanent magnet is rotationally supported and torquedthrough an angle by interacting magnetic fields produced by applicationof the electrical signal to a coil. In a moving magnet design,suspension is provided by the same techniques as in the DArsonval meter.Restoration can be provided by the use of a second, fixed magnettorquing the rotating magnet in a direction opposite to that from themotivation. Supplying motivation excitation is less of a problem sinceno signal must be applied to moving members. The movingmagnet design,however, has substantial performance defects. The meter torque is verynonlinear with applied signal and not consistently predictable from onemeter to the next. High magnet weight due to poor coupling, between themagnet and coil and low damping permit excessive meter wiggle." The poorcoupling also reduces meter efficiency and increases the disturbancesfrom magnet fields in the meter environment.

. around the BRIEF SUMMARY OF THE INVENTION In the present invention anelectrical meter of simple but accurate design is provided wherein theprimary features of motivation, restraint, and suspension are accurately provided by the interaction of simple elements in a meterstructure.

In a preferred embodiment, apermanent magnet is suspended by a knifeedge pivot to rotate through a predetermined angle. A fixed flux path isprovided be,- tween the poles of the permanent magnetand varies inreluctance with rotation of the magnet. Restoration re.- sults'frommagnetic forces between the rotatablemag: net and fixed flux pathrestraining the magnet to a stable angle of minimum reluctance. Thesesame forces provide the further benefit of applying a force bias to theknife edge suspension that improves its motional stability andsimplifies meter balancing. Motivation is provided by a coil woundaround the flux path and excited by the electrical signal beingmeasured. The coil current induces a secondary flux-within the fluxpaththat alters the permanent magnet flux accordingto itsdemagnetizationcurve and causes it to rotate to a new stable point ofdifferent flux pathreluctance as definec by the current in-the coil.

In a particular design implementation for the present invention, theflux path comprises a ferro magnetic ma.- terial of high permeabilityformed in first andsecond parallel arcs and placed slightly eccentric tothe axis of rotation of the permanent magnet to provide a small air gapbetween the magnet and ferro magnetic material which increases withrotation of the permanent magnet. The parallel arcs of ferromagneticmaterial may be viewed as separated from each other along the directionof the axis of rotation and have at one end a ferro magnetic spacercompleting the high permeability flux path from one to the other andhaving wound therecoil excited by the electrical signal being measured.

The knife edge suspension preferrably comprisestwo or more thin, lowpermeability metal vanes having small slots therein which permit thevanes to fit together in a somewhat loose fit that permits rotation, ofone vane with respect to the other. The permanent magnet is mounted onone vane while the other vane is secured to the meter housing. The fluxpath as structured above accepts a substantial portion of flux from thepermanent magnet passing from one pole thereof to the other and resultsin a force of attraction between the permanent magnet and the fluxpathwhich rotates the magnet to an angle of minimum air gap and biasesthe contacting knife edges of the two vanes to substantially eliminatethe motion resulting from the loose fit of the vanes. The flux path isclosely coupledto receive a substantial portion of the flux from thepermanent magnet and to enable theelectric signal applied to theencircling coil to efficiently alter the magnets flux and resultinglychange the point of operation of the magnet on its demagnetizationcurve.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features of theinvention will be more clearly understood by reference to the followingdetailed description of a preferred embodiment presented for purposes ofillustration, and not by way of limitation, and to theaccompanyingdrawings of which:

FIGS. 1A and 1B are partially pictorial and partially diagrammatic viewsof a meter according to the invention at different deflection angles;

FIG. 2 is a pictorial and diagrammatic view of the meter of FIGS. 1A and1B as viewed horizontally;

' FIG. 3 is a demagnetization curve for the magnet used with theinvention of FIGS. 1A and 18 indicating operating points at differentmeter deflection angles;

FIG. 4 is a sectional and diagrammatic view of the suspension system forthe meter of FIGS. 1A and 1B illustrating its interrelationship with themagnetic circuit;

FIG. 5 and FIG. 6 indicate the component parts of the suspension systemindicated in FIG. 4;

FIG. 7 is a close-up view of portions of the suspension system;

FIG. 8 and FIG. 9 are diagrammatic representations of the pivotingaction of the suspension system.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT In the conventionalDArsonval meter an electric coil is pivotallysuspended in a magneticfield which may be provided by either a permanent magnet or a secondcoil responsive to a constant current or the signal being measured. Thepivoting coil is excited by the signal to be measured and produces itsown magnetic field as a result. The interaction of the two fieldsproduces a torque on the pivoting coil causing it to rotate. An elasticrestraint, such as a spiral spring, restrains the rotation of the coilto provide a net deflection representative of the magnitude of thesignal measured. Such a system will provide a meter of extraordinaryaccuracy, but at a substantial cost due to the complexity andsophistication of the motivation, restoring, and suspension elements.

In the alternative moving magnet meter design, a large permanent magnetis rotationally supported with a meter pointer affixed to it. A coilexcited by the signal being measured is placed at some distance from themagnet to permit it to rotate and provide a magnetic field cross actingwith the magnets field to torque the magnet and swing the pointer acrossa scale. Restoration and suspension may be provided by conventionaldesigns, or restoration may be achieved by the magnetic force from asecond magnet appropriately placed. Meters of this design are typicallyless costly but possess significant performance defects due to the costcutting use of simple elements and a lack of functional cooperationsbetween component parts of the meter.

In accordance with the invention pictorially indicated in FIGS. 1A, 1Band 2, however, basic meter functions are more simply provided by theinterrelationship of a permanent magnet and a flux path to produce acombination of elements uniquely cooperating toward overall precisemeter performance. With specific reference to FIG. 1A, a permanentmagnet 12 is secured to a vane 14 to which is attached a pointer 16 forrotation over a scale 18. The vane 14 meshes with a vane 20 to providean axis of rotation 22 of the vane 14 relative to the vane 20. Vane 20is attached to a bracket 24 which is secured to the meter housing 26.

The magnet 12 has a tip 23 shaped to direct and concentrate the flux atthat point; preferable with a pointed shape slightly rounded for betterballistic characterisitcs. The tip of magnet 12 describes an arc 28 asthe vane 14 and magnet 12 rotate with respect to vane 20 through apredetermined angle, for example An arc of ferromagnetic material 30 isplaced slightly eccentric to the axis 22 and has its inner surface 31spaced just outside the are 28 to receive the concentrated flux directedfrom the tip of magnet 12. The distance between arc 28 and inner surface31 of the ferromagnetic material 30 increases with the angle of rotationof the magnet 12.

Thus, as indicated in FIG. 1B, the gap between the tip of the magnet 12and ferromagnetic material 30 is larger at an extreme angle ofdeflection of the magnet 12 than it is for a minimal angle of deflectionrepresented by FIG. 1A.

As can be seen from a horizontal view in FIG. 2, the ferromagneticmaterial is composed of top and bottom portions 30a and 30b. Aferromagnetic spacer 32 provides a high permeability flux path betweenthe top and bottom portions 30a and 30b at one end. As shown, spacer 32is located at the end. of largest gap or greatest angle of rotation forthe magnet 12 but may be at either end or elsewhere. The spacer 32 has acoil 34 wound around it and the coil is excited by the electrical signalbeing measured, such as from source 36. At the other end, a secondspacer 33, of nonmagnetic or magnetic characteristics, holds theportions30a and 30b spaced. An additional or alternate coil may be wound aroundportions 30a or 30b for improving sensitivity or achieving other desiredcharacteristics.

Shown in FIG. 2, the magnet 12 has an upper north pole and a lower southpole. Flux between the two poles is induced to travel through the upperportion 30a through the spacer 32 and through the lower portions 30b ina closed loop. By using a high permeability substance for the ferromagnetic material 300 and 30b and spacer 32, a substantial portion ofthe flux from the magnet 12 can be induced to travel through this fluxpath.

As is known, the permanent magnet 12, in the presence of a highpermeability material will exhibit a force attracting it to thatmaterial. In this case, the magnet 12 will be drawn toward portions 30aand 30b. Because the gap between the magnet and material varies withrotation of the magnet 12 the magnet will also experience a torqueurging it toward an angle of minimum gap between the ferro magneticmaterial 30 and the permanent magnet 12. By making the inner surface ofthe ferro magnetic material arcuate and providing a minimum gap at apoint of zero deflection of the pointer 16 on the scale 18, the magnet12 will stabilize at that point in the absence of any excitation signalapplied to the coil 34.

Referring now to FIG. 3, demagnetization curves are illustrated forexplaining the unique operation of the meter motivation in the presentinvention. The demagnetization curves of three typical permanent magnetsare presented; curve 40 represents the magnetization curve for a typicalalnico magnet, curve 42 for a LODEX (a trademark of the General ElectricCompany) magnet and curve 44 for a ceramic magnet. Curve 44 with therelatively more linear characteristics represents a more idealdemagnetization curve for use in the present system and will accordinglybe the curve used to explain the operation of the meter. A plurality ofmagnetic load lines 46, 48 and 50 radiate from the zero axis tointercept the demagnetization curve 44 at respective points 52, 54 and56. Also indicated in FIG. 3, a series of coil flux density drop-offlines 58, 60 and 62 represent operating points for the coil at differentcurrent levels and are drawn to intersect the points 52, 54 and 56respectively.

In operation only a small portion of the demagnetization curve betweenthe points 52 and 56 will be utilized to minimize nonlinearitiesresulting from the hysteresis curve and to prevent a permanent loss ofmagnetization in the ceramic magnet. From a point 52 of zero deflectionthe coil 34 is excited with a predetermined current and there is acorresponding change'in the field intensity within the magnetrepresented by vector 64. The system will balance to maintain itself onthe demagnetization curve 44 by cuasing a reduction in the flux densityB represented by vector 66 returning the system to a new point 68 on thecurve 44 which defines an angle of rotation 70 from zero line 46. Theopposite process occurs whenever the current is reduced in the coil 34It can be seen that a morelinear operation is achieved when the demagnetization curve is itself more linear, thoughchanges in linearity canbe programmed into the meter by adjusting the curvature of theferromagnetic material 30, or positioning of coil 34. In particular, inFIG. 1A it is desirable to flatten the curvature at the point 72 ofzero-deflection to reduce the tendency of the unexcited meter tooscillate about the zero point. Also, the curvature of the material 30is slowly reduced from a point of maximum meter deflection to minimumdeflection to control meter ballistics and prevent a too rapid return ofthe meter to zero deflection. A suitable choice of magnetic materials asindicated above will help to minimize the coil bias current necessary toinitiate meter motion by locating the load line 46 in FIG. 3 which is'afunction of magnetic materials and air gaps as close to the verticleaxis as possible. This bias current is thus kept a negligible quantity.

A magnet operating on these principles has many advantages. Due to aclose coupling between the permanent magnet 12 and flux path 30, thestrength and weight of the permanent magnet 12 is kept lower than wouldbe the case with prior art moving magnet meters. Meter wiggle isaccordingly eliminated as a significant problem. The lower magnet weightalso reduces pivot friction and the resulting meter hysteresis thatgives different indications for the same signal. The closer coupling, inaddition to providing a higher meter efficiency and greater sensitivity,also reduces the susceptibility of the meter to disturbances from strayfields or magnetic materials from the environment. A further advantageis in a reduction of temperature sensitivity attributable to oppositetemperature coefficients for the magnetic properties of magnet 12 andflux path 30 in the case of ceramic and ferromagnetic compositionsrespectively or other common materials for these elements.

Finally, the unique meter design of the present invention and the novelprinciples of operation permit sensitive meters of very small size. Inprior art moving'magnet meters, the meter torque is the mathematicalvector product of the coil field and the magnet field. Thus a large coiland magnet will be capable of greater fields and more sensitivity. Inthe present invention, however, torque is more dependent on geometricratios and induced flux effects on the demagnetization curve. Thispermits reducing magnet and meter size without a proportionate reductionin meter sensitivity.

Further details of a preferred suspension system and its advantages whenoperating with the meter of the invention can be seen with reference toFIG. 4. The ferromagnetic portions 30a and 30b are indicated in sectionat approximately the point of mid-scale in the meter deflection. Themagnet 12 is pictorially indicated positioned at the same point and hascemented thereto the vane 14. The vane 14 is shown more clearly in FIG.5 as having a central cut-out portion 76 through which the magnet 12fits and is cemented at its edges to shoulders which contact theperipheral portions of the vane 14 at 78 and 80. Slots 82 and 84 areprovided to straddle the vane 20 indicated in FIG. 4 and'FlG. 6. Thevane 20 also has slots 86 and 88 which straddle the vane 14, in eachcase the slots 82 and 86 and slots 84 and 88 fitting or meshingtogether. FIG. 7 indicates more clearly the nature in which the slots.fit showing slots 82 and 86 in the vanes 20 and 14 as they are arrangedtogether. Vane 20 may have reduced material in central portion 87 tofacilitate bending there for fitting the vanes together with minimumburring of the slot edges. Vanes 14 and 20 are normally fashioned from athin, nonmagnetic, resilient material such as beryllium-copper.

The width of the slots is sufficient to allow a substantial rotation ofone vane with respect to the other, typically 100. In FIG. 8 one slot,for example slot 86, is indicated in vane 20 straddling the vane 14. Ascan be seen, in order to allow a :50." angle of rotation, there must bea substantial gap in the slot 86. In all but extreme positions ofrotation the additional width to the gap allows the vanes to wigglesomewhat with respect to each other. It is desirable therefor to cut theedges of the gap at an angle as indicated in FIG. 9 to provide singlepoints of contact or knife edges rather than two points of contact orknife edges for each slot as indicated in FIG. 8. This allows the gap orwidth of the slot to be reduced slightly. The sharper point of contactalso improves the pivoting action and lowers friction. Even with theimproved form of FIG. 9, however, there is significant, unwanted,nonrotational motion or slop to the knife edge suspension due to thelooseness of fit.

The looseness of fit is a function of the difference between the gap 86distance in FIG. 9 and vane 14 8 thickness t. According to theapplicable equation cos a/2 t/g,

where a is the total desired rotation angle, the thickness to gap ratiois approximately 0.65 for a 100 total swing. For a typical vanethickness of IO mils the 3-! difference to slop is over 5 mils. At thetip of the meter pointer, this looseness could easily translate into amovement of a tenth of an inch or more.

This motion, however, is substantially eliminated in the invention bytheattraction of the magnet 12 to the ferromagnetic materials 30a and30b. This attraction results in a preload or bias on the slottedportions of the vanes forcing the vane 14 against the outer edge of theslots in the vane 20. While the force which produces this preload isreduced when the coil 44 is excited and during the time that the magnetis rotating to a new stable point, it is sufficient to providesignificant bias. This force bias also simplifies the meter balancingrequirements to the point where only a rough balance need be done.

Optionally, an additional piece of ferromagnetic material 90 may beadded between the portions 30a and 30b and outside of the magneticcircuit between the poles of the magnet 12 through portions 30a and 30band spacer 32. The gap from material 90 to magnet 12 may remainconstant. It is shown in FIG. 4.

Having described above a preferred embodiment of the invention, it willoccur to those skilled in the art that substantial adaptations,modifications and alterations can be made without departing from thespirit of the invention. The vanes 14 and 20, while preferrably of lowpermeability, nonmagnetic metal may be otherwise structured. A moreconventional suspension system may also be employed. Also linear orother motion in addition to rotation between teh magnet and the fluxpath may be employed. Linear motion can be achieved using a rolling orsliding guide to relatively support the magnet and flux path. It isaccordingly intended to limit the scope of the invention only asindicated in the following claims.

What is claimed is:

1. A permanent magnet meter operating in response to an electricalsignal and comprising:

a magnet;

means responsive to said electrical signal for inducing a magnetic fluxrepresentative of said electrical signal;

means for positioning said flux inducing means and operative to directflux in opposite directions between said magnet and said flux inducingmeans in a close coupling arrangement and to produce an alteration inthe flux from said magnet in accordance with the demagnetization curvethereof in response to flux induced by said electrical signal; and

means for supporting said magnet to allow relative motion between saidmagnet and said directing means;

said positioning means being adapted to provide a stable position forsaid magnet relative to said inducing means with said stable positionbeing a function of the flux induced by said electrical signal.

2. A meter responsive to electrical signals to provide an indication ofthe magnitude thereof comprising:

a flux source;

a flux path for a substantial portion of the flux of said flux source;means for supporting said flux path and said flux source to providerelative motion therebetween;

said flux path being adapted to vary its reluctance to the flux fromsaid source with relative position of said source so as to provide arestoring force urging said source to a stable position relative to saidflux path as a result of the magnetic attraction between said source andsaid flux path;

means for impressing a flux in said flux path in response to saidelectrical signal to oppose the flux of said flux source whereby thestable position of said flux source with respect to said flux path iscaused to vary, producing a motion of said source with respect to saidflux path to a new stable position.

3. A permanent magnet meter operative to indicate the magnitude of anelectrical signal and comprising:

a permanent magnet;

a flux path operative to accept a portion of the flux induced by saidmagnet at one pole and to return said flux to said magnet at anotherpole;

means for mounting said permanent magnet with its pole faces toward saidflux path to allow motion of said magnet relative to said flux path;

the relative mounting of said flux path providing a gap between saidpath and the pole faces of said magnet which varies with relativeposition of said permanent magnet; and

means for applying a variable flux to said flux path with a polaritywhich opposes the flux of said permanent magnet, and operative togenerate said variable flux to represent said electrical signal;

said variable flux being operative to cause relative motion of saidmagnet thereby to provide an indication of said electrical signal.

4. A permanent magnet meter responsive to electrical signals to providean indication of the magnitude thereof comprising:

a permanent magnet; a flux path for a portion of the flux of saidpermanent magnet; means for supporting said flux' path and saidpermanent magnet to provide rotation therebetween; said flux path beingadapted to vary its reluctance to said permanent magnet flux withrotation thereof so as to provide a restoring torque to a stable angleof rotation resulting from the magnetic attraction between said magnetand said flux path;

means for impressing a flux in said flux path in response to saidelectrical signal in a direction to oppose flux in said permanent magnetwhereby the stable angle of said permanent magnet with respect to Saidflux path is caused to vary, producing a rotation of said magnet withrespect to said flux path.

5. The permanent magnet meter of claim 4 wherein:

said means for supporting said permanent magnet includes a plurality ofthin vanes which are adapted to mesh with each other in a loose fit toallow rotation of said plurality of vanes with respect to each other;and

said permanent magnet is affixed to one of said vanes whereby motionpermitted by the looseness of fit of said plurality of vanes is reducedby the attraction force of said permanent magnet to said flux path.

6. The permanent magnet meter of claim 4 wherein said permanent magnetis a ceramic magnet.

7. The permanent magnet meter of claim 4 wherein ,said permanent magnetis shaped to concentrate and direct its flux toward said flux path.

8. A permanent magnet meter operative to provide an indication of themagnitude of an electrical signal and comprising: i

a permanent magnet;

a flux path for at least a portion of the flux from said permanentmagnet;

means for pivotally mounting said magnet with respect to said flux pathand including two or more slotted vanes having their slots fit togetherto permit said vanes to rotate with respect to each other throughout apredetermined angle;

said permanent magnet being secured to at least one of said vanes in anorientation to provide magnetic attraction between said permanent magnetand said flux path and to urge a rotation between said magnet and saidflux path to a stable angle, the fitted slots of said plurality of vanesbeing thus urged against each other by the attraction of said permanentmagnet to said flux path whereby the motion produced by the looseness offit between said plurality of vanes required to permit rotation thereofis reduced; and

means for applying a flux to said flux path in a polarity substantiallyto oppose the flux of said permanent magnet, said applied flux beingrepresentative of said electrical signal and operative to vary thestable angle of rotation of said magnet with respect to said flux path.

9. The permanent magnet meter of claim 8 wherein one or more of saidvanes is shaped to permit ease in fitting together the slots of saidvanes without substantial burring of the edges of said slots.

10. A permanent magnet meter operative to indicate the magnitude of anelectrical signal and comprising:

a permanent magnet;

means for supporting said permanent magnet to allow rotation thereofabout an axis;

a flux path operative to accept a portion of the flux from said magnetat one pole and to return said flux to said magnet at another pole;

said flux path arcing about theaxis of rotation of said permanent magnetwith a gap between the inner surfaces of said flux path and the outersurface of said magnet; 7

said flux path being oriented to provide a variation in said gap withrotation of said permanent'magnet; and

means for applying a flux to said flux path with a polarity to opposethe flux of said permanent magnet, said applied flux beingrepresentative of said electrical signal and effective to cause rotationof said magnet to maintain said magnet on its demagnetization curve.

11. The permanent magnet meter of claim 10 wherein:

said means for supporting said permanent magnet includes a plurality ofthin vanes which are adapted to mesh with each other in a loose fit toallow rotation of said plurality of vanes with respect to each other;and

said permanent magnet is affixed to one of said vanes whereby motionpermitted by the looseness of fit of said plurality of vanes is reducedby the attraction force of said permanent magnet to said flux path.

12. The permanent magnet meter of claim 10 wherein said permanent magnetisa ceramic magnet.

13. The permanent magnet meter of claim 10 wherein said permanent magnetis shaped to concentrate and direct its flux toward said flux path.

14. The permanent magnet meter of claim 10 further including a secondflux path providing a gap with said magnet, said second flux path beingsubstantially outside the flux circuit of the first mentioned flux path.

15. A meter operative to provide an indication of the magnitude of anelectrical signal and comprising:

means for providing a magnetic flux; Y,

means for rotationally supporting said magnetic flux providing means toallow rotation of said magnetic flux providing means about an axis;

a flux path positioned to accept at least a portion of the flux fromsaid magnetic flux providing means and to provide a variation in thereluctance of said flux path with rotation of said flux providing meansso as to provide a restoring torque and a stable angle of rotationbetween said magnetic flux providing means and said flux path;

means operative in response'to said electrical signal to apply fluxrepresentative of said signal through said flux path to oppose the fluxof said flux producing means thereby to produce a variation in torquebetween said flux producingmeans and said flux path as a result of fluxfrom said flux providing means and said flux applying means whereby anangle of zero torque between said flux providing means and said fluxpath varies with said electrical signal.

16. The permanent magnet meter of claim 8 wherein said permanent magnethas a relatively linear demagnetization curve.

17. The permanent magnet meter of claim 8 wherein:

said flux path includes first and second arcuate magnetic elementshaving first and second concave surfaces respectively; and means forsecuring said first and second elements to each other in parallel spacedrelationship and for providing a high permeability flux paththerebetween; and

said permanent magnet includes a tip arranged with respect to saidpivotally mounting means whereby said tip describes an arcuate path uponrotation of said magnet;

said first and second elements being disposed with their concavesurfaces facing said tip of said permanent magnet and spaced from saidarcuate path by a gap which continuously increases from a minimum gap.

18. The permanent magnet meter of claim 17 wherein said tip portion ofsaid permanent magnet is generally rounded.

19. The permanent magnet meter of claim 17 wherein said first and secondconcave surfaces of said first and second arcuate magnetic elements areslightly flattened at said point of minimum gap.

20. An electrical meter operative to provide an indication of themagnitude of an electrical signal and comprising:

a magnet having a tip portion;

means for pivotally mounting-said magnet to allow rotation thereofthrough a predetermined angle; the tip portion of said magnet defininga'circular are as said magnet rotates; first and second arcuate magneticelements having respective first and second concavesurfaces;

means for securing said first and second elements together and providinga high permeability flux path therebetween;

means for mounting the secured first andsecond arcuate elements relativeto the pivotal axis of said magnet with said first and second concavesurfaces facing said magnet with a spacing betweensaid circular arc andsaid concave surfaces which-continuously increases from a point ofminimum gap; and means for inducing a magnetic flux in said first andsecond elements in response to said electrical signal in a direction tooppose the flux-of said magnet. 21. The electrical meter of claim 20wherein said flux inducing meansincludes a coil enclosing said means forsecuring said first and second arcuate elements.

22. The electrical meter of claim 20 whereinsaid magnet has first andsecond magnetic poles respectively facing the firstand second concavesurfaces of said first and second elements wehreby magnet flux betweensaid poles is directed through said first and-second elements and saidhigh permeability securing means.

23. The electrical meter of claim and further in cluding a pointersupported to rotate with said magnet and provide an indication of theangle of rotation of said magnet in response to flux induced by saidelectrical signal.

24. A magnet meter for indicating the magnitude of a signal comprising:

a first flux source;

a second flux source having a flux responsive in magnitude to saidsignal;

a magentic circuit for the fluxes of said first and second flux sources;

means for supporting said first flux source for relative motion withrespect to said magnetic circuit;

said magnetic circuit including:

means for applying the flux from said second flux source to said firstflux source in opposition to the flux of said first flux sourcethroughout a range of positions of said first flux source with respectto said magnetic circuit;

means responsive to the position of said first flux source for producingcorrespondingly different values of reluctance in said magnetic circuitto the fluxes from said first and second flux sources whereby said firstflux source has a stable position in said range of positionsrepresentative of the magnitude of said signal, said stable positionrepresenting a position of minimum reluctance. 25. A meter responsive toelectrical signals to provide an indication of the magnitude thereofcomprising:

a flux source;

a flux path for a substantial portion of the flux of said flux sourceand including an arctuate magnetic arm positioned to accept flux fromsaid flux source;

means for supporting said flux path and said flux source to providerelative motion therebetween;

said flux path being adapted to vary its reluctance to the flux fromsaid source with relative position of said source so as to provide arestoring force urging said source to a stable position relative to saidflux path as a result of the magnetic attraction between said source andsaid flux path;

means for impressing a flux'in said magnetic arm in response to saidelectrical signal whereby the stable position of said flux source withrespect to said flux path is caused to vary over a range producing amotion of said source with respect to said flux path to a new stableposition within said range;

said flux impressing means including means for providing said flux insaid arctuate magnetic arm below saturation for said arm over said rangein its response to the impressed flux from said electrical signal.

1. A permanent magnet meter operating in response to an electricalsignal and comprising: a magnet; means responsive to said electricalsignal for inducing a magnetic flux representative of said electricalsignal; means for positioning said flux inducing means and operative todirect flux in opposite directions between said magnet and said fluxinducing means in a close coupling arrangement and to produce analteration in the flux from said magnet in accordance with thedemagnetization curve thereof in response to flux induced by saidelectrical signal; and means for supporting said magnet to allowrelative motion between said magnet and said directing means; saidpositioning means being adapted to provide a stable position for saidmagnet relative to said inducing means with said stable position being afunction of the fluX induced by said electrical signal.
 2. A meterresponsive to electrical signals to provide an indication of themagnitude thereof comprising: a flux source; a flux path for asubstantial portion of the flux of said flux source; means forsupporting said flux path and said flux source to provide relativemotion therebetween; said flux path being adapted to vary its reluctanceto the flux from said source with relative position of said source so asto provide a restoring force urging said source to a stable positionrelative to said flux path as a result of the magnetic attractionbetween said source and said flux path; means for impressing a flux insaid flux path in response to said electrical signal to oppose the fluxof said flux source whereby the stable position of said flux source withrespect to said flux path is caused to vary, producing a motion of saidsource with respect to said flux path to a new stable position.
 3. Apermanent magnet meter operative to indicate the magnitude of anelectrical signal and comprising: a permanent magnet; a flux pathoperative to accept a portion of the flux induced by said magnet at onepole and to return said flux to said magnet at another pole; means formounting said permanent magnet with its pole faces toward said flux pathto allow motion of said magnet relative to said flux path; the relativemounting of said flux path providing a gap between said path and thepole faces of said magnet which varies with relative position of saidpermanent magnet; and means for applying a variable flux to said fluxpath with a polarity which opposes the flux of said permanent magnet,and operative to generate said variable flux to represent saidelectrical signal; said variable flux being operative to cause relativemotion of said magnet thereby to provide an indication of saidelectrical signal.
 4. A permanent magnet meter responsive to electricalsignals to provide an indication of the magnitude thereof comprising: apermanent magnet; a flux path for a portion of the flux of saidpermanent magnet; means for supporting said flux path and said permanentmagnet to provide rotation therebetween; said flux path being adapted tovary its reluctance to said permanent magnet flux with rotation thereofso as to provide a restoring torque to a stable angle of rotationresulting from the magnetic attraction between said magnet and said fluxpath; means for impressing a flux in said flux path in response to saidelectrical signal in a direction to oppose flux in said permanent magnetwhereby the stable angle of said permanent magnet with respect to saidflux path is caused to vary, producing a rotation of said magnet withrespect to said flux path.
 5. The permanent magnet meter of claim 4wherein: said means for supporting said permanent magnet includes aplurality of thin vanes which are adapted to mesh with each other in aloose fit to allow rotation of said plurality of vanes with respect toeach other; and said permanent magnet is affixed to one of said vaneswhereby motion permitted by the looseness of fit of said plurality ofvanes is reduced by the attraction force of said permanent magnet tosaid flux path.
 6. The permanent magnet meter of claim 4 wherein saidpermanent magnet is a ceramic magnet.
 7. The permanent magnet meter ofclaim 4 wherein said permanent magnet is shaped to concentrate anddirect its flux toward said flux path.
 8. A permanent magnet meteroperative to provide an indication of the magnitude of an electricalsignal and comprising: a permanent magnet; a flux path for at least aportion of the flux from said permanent magnet; means for pivotallymounting said magnet with respect to said flux path and including two ormore slotted vanes having their slots fit together to permit said vanesto rotate with respect to each other throughout a predetermined angle;said permanent magnet being Secured to at least one of said vanes in anorientation to provide magnetic attraction between said permanent magnetand said flux path and to urge a rotation between said magnet and saidflux path to a stable angle, the fitted slots of said plurality of vanesbeing thus urged against each other by the attraction of said permanentmagnet to said flux path whereby the motion produced by the looseness offit between said plurality of vanes required to permit rotation thereofis reduced; and means for applying a flux to said flux path in apolarity substantially to oppose the flux of said permanent magnet, saidapplied flux being representative of said electrical signal andoperative to vary the stable angle of rotation of said magnet withrespect to said flux path.
 9. The permanent magnet meter of claim 8wherein one or more of said vanes is shaped to permit ease in fittingtogether the slots of said vanes without substantial burring of theedges of said slots.
 10. A permanent magnet meter operative to indicatethe magnitude of an electrical signal and comprising: a permanentmagnet; means for supporting said permanent magnet to allow rotationthereof about an axis; a flux path operative to accept a portion of theflux from said magnet at one pole and to return said flux to said magnetat another pole; said flux path arcing about the axis of rotation ofsaid permanent magnet with a gap between the inner surfaces of said fluxpath and the outer surface of said magnet; said flux path being orientedto provide a variation in said gap with rotation of said permanentmagnet; and means for applying a flux to said flux path with a polarityto oppose the flux of said permanent magnet, said applied flux beingrepresentative of said electrical signal and effective to cause rotationof said magnet to maintain said magnet on its demagnetization curve. 11.The permanent magnet meter of claim 10 wherein: said means forsupporting said permanent magnet includes a plurality of thin vaneswhich are adapted to mesh with each other in a loose fit to allowrotation of said plurality of vanes with respect to each other; and saidpermanent magnet is affixed to one of said vanes whereby motionpermitted by the looseness of fit of said plurality of vanes is reducedby the attraction force of said permanent magnet to said flux path. 12.The permanent magnet meter of claim 10 wherein said permanent magnet isa ceramic magnet.
 13. The permanent magnet meter of claim 10 whereinsaid permanent magnet is shaped to concentrate and direct its fluxtoward said flux path.
 14. The permanent magnet meter of claim 10further including a second flux path providing a gap with said magnet,said second flux path being substantially outside the flux circuit ofthe first mentioned flux path.
 15. A meter operative to provide anindication of the magnitude of an electrical signal and comprising:means for providing a magnetic flux; means for rotationally supportingsaid magnetic flux providing means to allow rotation of said magneticflux providing means about an axis; a flux path positioned to accept atleast a portion of the flux from said magnetic flux providing means andto provide a variation in the reluctance of said flux path with rotationof said flux providing means so as to provide a restoring torque and astable angle of rotation between said magnetic flux providing means andsaid flux path; means operative in response to said electrical signal toapply flux representative of said signal through said flux path tooppose the flux of said flux producing means thereby to produce avariation in torque between said flux producing means and said flux pathas a result of flux from said flux providing means and said fluxapplying means whereby an angle of zero torque between said fluxproviding means and said flux path varies with said electrical signal.16. The permanent magnet meter of claim 8 wherein said permanenT magnethas a relatively linear demagnetization curve.
 17. The permanent magnetmeter of claim 8 wherein: said flux path includes first and secondarcuate magnetic elements having first and second concave surfacesrespectively; and means for securing said first and second elements toeach other in parallel spaced relationship and for providing a highpermeability flux path therebetween; and said permanent magnet includesa tip arranged with respect to said pivotally mounting means wherebysaid tip describes an arcuate path upon rotation of said magnet; saidfirst and second elements being disposed with their concave surfacesfacing said tip of said permanent magnet and spaced from said arcuatepath by a gap which continuously increases from a minimum gap.
 18. Thepermanent magnet meter of claim 17 wherein said tip portion of saidpermanent magnet is generally rounded.
 19. The permanent magnet meter ofclaim 17 wherein said first and second concave surfaces of said firstand second arcuate magnetic elements are slightly flattened at saidpoint of minimum gap.
 20. An electrical meter operative to provide anindication of the magnitude of an electrical signal and comprising: amagnet having a tip portion; means for pivotally mounting said magnet toallow rotation thereof through a predetermined angle; the tip portion ofsaid magnet defining a circular arc as said magnet rotates; first andsecond arcuate magnetic elements having respective first and secondconcave surfaces; means for securing said first and second elementstogether and providing a high permeability flux path therebetween; meansfor mounting the secured first and second arcuate elements relative tothe pivotal axis of said magnet with said first and second concavesurfaces facing said magnet with a spacing between said circular arc andsaid concave surfaces which continuously increases from a point ofminimum gap; and means for inducing a magnetic flux in said first andsecond elements in response to said electrical signal in a direction tooppose the flux of said magnet.
 21. The electrical meter of claim 20wherein said flux inducing means includes a coil enclosing said meansfor securing said first and second arcuate elements.
 22. The electricalmeter of claim 20 wherein said magnet has first and second magneticpoles respectively facing the first and second concave surfaces of saidfirst and second elements wehreby magnet flux between said poles isdirected through said first and second elements and said highpermeability securing means.
 23. The electrical meter of claim 20 andfurther including a pointer supported to rotate with said magnet andprovide an indication of the angle of rotation of said magnet inresponse to flux induced by said electrical signal.
 24. A magnet meterfor indicating the magnitude of a signal comprising: a first fluxsource; a second flux source having a flux responsive in magnitude tosaid signal; a magentic circuit for the fluxes of said first and secondflux sources; means for supporting said first flux source for relativemotion with respect to said magnetic circuit; said magnetic circuitincluding: means for applying the flux from said second flux source tosaid first flux source in opposition to the flux of said first fluxsource throughout a range of positions of said first flux source withrespect to said magnetic circuit; means responsive to the position ofsaid first flux source for producing correspondingly different values ofreluctance in said magnetic circuit to the fluxes from said first andsecond flux sources whereby said first flux source has a stable positionin said range of positions representative of the magnitude of saidsignal, said stable position representing a position of minimumreluctance.
 25. A meter responsive to electrical signals to provide anindication of the magnitude thereof comprising: a flux source; a fluxpath for a substantial portion of the flux of said flux source andincluding an arctuate magnetic arm positioned to accept flux from saidflux source; means for supporting said flux path and said flux source toprovide relative motion therebetween; said flux path being adapted tovary its reluctance to the flux from said source with relative positionof said source so as to provide a restoring force urging said source toa stable position relative to said flux path as a result of the magneticattraction between said source and said flux path; means for impressinga flux in said magnetic arm in response to said electrical signalwhereby the stable position of said flux source with respect to saidflux path is caused to vary over a range producing a motion of saidsource with respect to said flux path to a new stable position withinsaid range; said flux impressing means including means for providingsaid flux in said arctuate magnetic arm below saturation for said armover said range in its response to the impressed flux from saidelectrical signal.